Why does the Earth rotate slightly faster over three days this summer?
On July 9th, July 22nd and August 5th, the Earth spins a little faster, and those days are slightly shorter than 24 hours.
CBC -Canadian National News
- August 5, 2025 is one of the shortest days of the year, and is projected to be about 1.34 ms shorter than the 24 hours.
- Scientists attribute this phenomenon to changes in the effects of Earth’s nuclear and atmospheric.
- Although not perceptible to humans, these millisecond variations can affect systems that rely on atomic clocks and precise timekeeping.
If you don’t seem to get past your to-do list on August 5th, there’s at least an excuse.
Tuesday is predicted to be one of the shortest days of the year, marking the latest time the Earth can cut the day by more than a millisecond.
Scientists predict that August 5 will be 1.34 ms shorter, according to the US Navy Observatory issued by International Earth Rotation and Reference Systems Services and Timeanddate.
According to data published by TimeanDate, the millisecond mark has broken several times this year, and it’s recently July 11th.
Observation data revealed that July 22 was predicted to be shorter than 1 ms, so the predictions don’t always pass, but the data revealed that only 0.87 ms were shaved.
The Earth takes 24 hours to complete a full rotation on a standard day, equivalent to just 86,400 seconds.
Until 2020, the shortest day recorded on an atomic clock was 1.05ms short. In other words, Earth has completed a day’s rotation 1.05 ms less than the expected 86,400 seconds.
“Since then, Earth has been able to crush this old record by about half each year,” astrophysicist Graham Jones wrote for TimeanDate.
The shortest day ever recorded occurred on July 5, 2024, 1.66ms shortfall. The shortest day recorded this year was July 10th, a shorter 1.37ms.
Why is this happening?
According to Scientific American, the Earth’s rotation is affected by the core and the atmosphere.
Science Magazine says the core spin is slowing down for unknown reasons. This means that the rest of the planets must be speeded up to compensate.
“The core changes the speed at which the Earth rotates in hundreds of years over a decade,” Duncan Agnew, a geophysicist at the Institute of Oceanography, told the magazine. “This core has slowed down for the past 50 years, and as a result, the Earth is speeding up.”
According to Scientific American, the forces of the atmosphere speed up the Earth’s rotational speed in the summer of the Northern Hemisphere. The forces caused by the moon also affect the speed at which the Earth rotates.
The magazine points out that on a geological timescale, the Earth is slowing down, with rotations taking 70 million years ago and 300,000 years ago.
Do speed-up days stand out?
Of course, you will not notice any differences between the 24-hour standard standards.
However, scientists who track and operate atomic clocks may be facing a bit of a challenge.
First introduced in the 1950s, atomic clocks replaced how scientists previously measured the length of a day by tracking the rotation of the Earth and the position of the sun. The clock can also be measured in seconds or billions of nanoseconds that are globally synchronized to Universal Time (UTC).
If even a small amount of clocks are discarded, computers, servers, GPS signals, and other networks that depend on the exact time, David Gozard, an experimental physicist at the University of Western Australia, told the Guardian.
